Electrically operated shutter



United States Patent O 3,252,318 ELECTRICALLY OPERATED SHU'ITER Fred D. Rosen, La Habra, Calif., assignor to North American Aviation Inc. Filed (let. 7, 1963, Ser. No. 314,394 11 Claims. (Cl. 73-12) This invention relates to an electrically operated shutter, and more particularly, to a shutter capable of controlled timing.

In order to study the impact characteristics of high velocity particles on various materials it is necessary to accelerate the particles to very high velocities. A convenient tool for this acceleration is an electrically operated accelerator wherein a large amount of electrical energy is delivered to an arc which causes an explosion of material to either push or drag particles. Because of the very high temperatures and pressures and the high gas flow rates present in such accelerators the desired particles are often accompanied by extraneous materials such as portions of the accelerator itself. It is a general characteristic of the extraneous materials that the mass is larger or the starting time later than the particles of interest so that the velocity of these materials is less than the velocity of the desired particles. Additionally when accelerating a plurality of particles, a range of velocities is obtained and usually the particles of interest are those having the highest velocity.

At some point along the flight path of the particles from the accelerator the particles of interest will be appreciably in front of the extraneous materials traveling along the ilight path. It is therefore desirable to obstruct the ilight path at a predetermined time after tiring of the accelerator so -that the particles of interest may freely pass and the extraneous materials be obstructed. The velocity range that is of most interest in the study of high velocity impact ranges upward of 30,000 feet per second. Therefore a very fast means of obstructing the path is required.

In a study of high velocity impact it is usually desirable to study several impact points from particles traveling over a broad spectrum of velocities. However, to avoid ambiguities it is desirable to have very few target impacts from any single firing of the accelerator system. The velocity of the fastest accelerated projectiles is readily controlled in the accelerator :and lower speed particles should be removed to eliminate the ambiguities arising when multiple impacts occur on the target. Therefore it is desirable to actuate a shutter at a predetermined period of time after operation of the accelerator so that only the highest velocity particles impact on the target. None of the yavailable prior art shutters have aiforded suflicient variable time control to separate particles over a spectrum of high velocities. The available shutters have not been capable of operating in the very short time intervals involved with the reproducibility and control desired.

It is therefore a broad object of this invention to provide a shutter overcoming these deficiencies.

Thus in the practice of this invention according to a preferred embodiment there is provided an electrically operated accelerator for accelerating particles along a ilight path. On the ight path there is a member having an aperture through which the desired particles may pass. A non-magnetic metal tiap is pivotally mounted on the member adjacent to the aperture so as to be able to swing into a position obstructing the aperture. A coil is arranged next to the iiap so that when a heavy current passes through the coil an eddy current is induced in the flap. The field from the coil current and the iield from the eddy current interact to repel the ap and swing it into a position obstructing the aperture. A

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variable source of current is provided so that the time required to close the shutter can be controlled and a timer is also provided to verify the operation of the shutter.

Thus it is a broad object of this invention to provide an electrically operated shutter.

It is another object of this invention to provide a shutter with fast response time.

It is an additional object of this invention to provide a shutter with controlled response time.

It is another object of this invention to provide a means for separating higher velocity particles from lower velocity particles.

It is an object of this invention to provide an accelerator for high velocity particles.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein a shutter assembly is illustrated in a particle accelerator.

The drawing illustrates an accelerator system including a shutter incorporating the principles of this invention. As illustrated in this embodiment there is provided an accelerator 10 which is electrically operated by means of the rapid discharge of a capacitor 11. The charge on the capacitor is regulated by a variable D.C. power supply 36. Ihe accelerator comprises a tubular piece or gun barrel 37 'along which particles to be accelerated can travel for directing the initial portion of their flight. In a preferred embodiment the gun barrel is electrically connected to the one side of the capacitor. An electrode 38 is electrically connected to the other side of the capacitor, A metal wire 39, preferably of lithium or other light metal, is provided between the electrode and the metal gun barrel. A thin sheet dielectric material 4l such as oriented polyethylene terephthalate (Mylar) is provided between the end of the lithium wire and the gun barrel. The other end of the lithium wire is in contact with the electrode 38. Thus, a complete electric circuit including the capacitor, electrode, lithium wire and gun barrel is provided except for the short portion interrupted by the dielectric iilm 4l. The lithium wire is contained in a ceramic cylinder 42 which closely lits around the wire and serves to space the electrode and gun barrel apart. A strong metal pressure jacket 43 surrounds the ceramic insert to contain the high pressures generated during operation of the accelerator.

In operation of the accelerator a number of small particles are suspended on the dielectric film 41 in line with the passage through the accelerator tube 37. In order to accelerate the particles, the charge on the capacitor 11 is gradually increased to several thousand volts until a dielectric breakdown occurs in the dielectric film at which instant a very large current flows through the lithium wire. The magnitude of the current is such that the lithium Wire explodes and is completely vapo-rized and heated to an extremely high temperature. The exploding lithium wire provides a large volume of low molecular Weight gas which streams through the gun barrel at very high velocity. The particles suspended on the dielectric iilm 41 are entrained in the flowing gas and aerodynamically accelerated to very high velocities. The very high pressures generated in the accelerator upon explosion of the lithium wire are contained by the ceramic sleeve and the metal jacket. A typical accelerator of the type described is illustrated in further detail in a co-pending application entitled Accelerator by E. A. Escallier and C. N. Scully, Serial Number 283,202 and assigned to North American Aviation, Inc., the assignee of the present application.

After the rapidly expanding gas has passed through the gun barrel 37 ,and accelerated the particles to very high velocity the gas expands radially and its velocityr decreases. However, the particles accelerated continue at very high velocity and pass along a ight path 12 and impinge on a target 13. The particles accelerated exhibit a spectrum of velocities due to the non-uniform ilow characteristics of the metal vapor across `the cross section of the gun barrel and other diiferences in the interaction of the particles with the high velocity expanding metal vapor. At some xed point in the flight path between the accelerator and the target a batlie member 14 is provided having an aperture 16 through which the particles may pass. Arranged adjacent this aperture is a shutter assembly 17 for obstructing the flight path at a prearranged time. It is preferred that the passage through the gun barrel, the target and the flight path therebetween be maintained in vacuum during operation of the accelerator. Thus, a fixed connection is provided between the accelerator and the target. The baille member 14 and the shutter assembly are lixedly secured to the connection so that it is spaced a known distance from the accelerator. Further details of this connection and vacuum system are shown in the ab-ove mentioned co-pending application of E. A. Escallier et al.

It is convenient to arrange the member 14 about three feet from the accelerator portion of the apparatus. Useful information on the impact of high velocity particles is obtained for virtually any particle over about 30,000 feet per second. Thus, the particles of interest will pass through the aperture approximately 100 microseconds after electrical initiation of the exploding lithium wire. Ambiguity is introduced in the results obtained when the target is impacted by particles traveling at velocities appreciably below the velocity of the fastest particles. This provides a large number of impact craters which lead to uncertainty in analysis of the results. Thus, it is desirable to operate the shutter assembly so that the aper- -ture is obstructed after about 100 microseconds and preferably before about 200 microseconds so that particles traveling at less than about 15,000 feet per second will not impact upon the target.

The shutter assembly comprises a ap 18 pivotally attached to the baille member 14 adjacent -to the aperture so that the flap -is free to move between a position leaving the ight path unobstructed and a second position, shown in phantom, wherein the flight path is obstructed. A light spring 19 is provided between the member 14 and the ap so as to resiliently bias the flap into a position leaving the ight path unobstructed. The ilap is located on the same side of the member 14 as the accelerator. Thus any particles traveling along the ight path 'after the flap has obstructed part of the flight path will strike the tlap in such a way as to urge the ap toward the closed position rather than toward the open position.

The flap is preferably constructed of a flat sheet of aluminum or other light weight non-magnetic electrically conductive material. The ap can also incorporate stitfening ridges or corrugations for greater rigidity when thin sheet is used in the construction. It is desirable to keep the weight of the ap low so that a high speed operation can be obtained. Additionally it is necessary that the material be non-magnetic in order for eddy current repulsion to be effective to operate the shutter at high speed.

When the shutter is -in the open position as illustrated in the drawing the flap rests against a cylindrical insulating coil form 21. It is convenient to arrange this coil form so that the plane of the ap when resting against the coil form is substantially perpendicular to the plane of the bale member through which the aperture penetrates. The edge of the ap nearer the accelerator should be close to the Hight path so that a minimum travel is required to obstruct the flight path in order that high speed operation can be obtained. No gain is obtained by canting the ap so that it tilts toward the closed position and a 4 distinct loss is noted if the tiap is canted away from the flight path.

A coil 22 of insulated heavy copper wire is wrapped on the coil form so that the axis of the coil is normal -to the plane of the ap. A thin portion of the coil form insulates the flap from the coil. One end of the coil is electrically connected with a capacitor 23 and the other end of the coil is electrically connected to the anode of an ignitron tube 24. The cathode of the ignitron is in turn electrically connected to the capacitor 23. An ignitron is a well known cold cathode electron tube of the mercury arc type. The cathode comprises a pool of mercury and a special igniter electrode dips into the mercury. The igniter is a rough surface material that `is not wetted by mercury, such as tungsten. A small current flowing between the igniter and the mercury results in a very high current density on the points of lthe rough spots, and a small cathode spot is formed. This is sutlicient to initiate current flow to the anode and the tube can then conduct a large current. A typical ignitron suitable for use in the practice of this invention is a model GL7171 available from General Electric Company. A conventional gap switch, transistor, or other voltage initiated high current device can be used in place of the ignitron tube. An

induction lcoil 27 is provided adjacent the current carrying connections to the accelerator so that a current is induced therein when a heavy current flows through the accelerator. The induction coil is connected to the cathode and the igniter of the ignitron to serve as a trigger. The current induced in the induction coil initiates conduction in the ignitron.

The charge on the capacitor 23 is regulated and selected by a variable D.C. power supply 28 so that a predetermined voltage can be applied across the capacitor, and a predetermined current passed through the coil upon discharge of the capacitor. The time between operation of the accelerator and closing of the shutter is determined by the charge upon the capacitor 23, higher charging voltages giving faster times. Thus instead of employing a complicated electronic delay circuit to effect closure after a certain elapsed time, the time is regulated by the velocity of mechanical motion obtained when the motion is initiated at a substantially fixed instant of time. That is, the initiation of current llow due to discharge of the capacitor occurs in a uniform time interval after operation of the accelerator. In the illustrated embodiment the time interval is small, in the order of four microseconds or less. The force acting on the ap and hence its acceleration are dependent on the current flow, thus regulating the total time interval between operation of the accelerator and shutter closure.

On the same side of the member 14 as the flap and on the opposite side of the aperture there is provided a sponge rubber bumper 29 against which the ap touches when in a position obstructing the llight path as shown in phantom in the drawing. An electrical -contact plate 31 is provided on the face of the bumper so that electrical contact is made with the flap when it reaches this position obstructing the flight path. A timer 32 is electrically connected to the Contact plate. Additionally, electrical contact is made with the ap itself so that a complete circuit is formed when the ap is in the position touching the contact plate. The timer is also connected to the induction coil 27 so that the time interval between the tiring of the accelerator 10 and the contact between the plate 31 and -the ap 18 can be obtained. Any conventional timer capable of measuring small fractions of a second lis suitable for this application. A suitable timer is a laboratory oscilloscope.

The accelerator is operated by means of a very heavy electric current supplied by the capacitor 11. Shortly after the current commences flowing through this circuit to explode the wire the particles of interest are accelerated along the flight path 12 along with any extraneous materials as hereinabove described. The current ilowing through the accelerator is sensed by induction coil 27 which initiates conduction in the ignitron tube 24. This closes the circuit including the coil 22 and the capacitor 23 permitting a current to flow through the coil. The magnitude of the current is determined by the charge put on the capacitor 23. Heavy gauge wire is emloyed in the coil so that the resistance is low and a heavy current can ow. Likewise the coil form is made of non-magnetic material so that a minimum impedance to the rapidly increasing current is imposed. If magnetic material is employed a large inductance is present which limits the rate of current rise and the maximum current, thereby reducing the operating speed of the shutter. The large current ilowing through the coil induces an eddy current in the non-magnetic flap. A substantial eld accompanies each of these currents and the elds interact to cause a repulsion between the coil and the flap. This repulsion causes the pivotally mounted flap to pivot so as to obstruct the tlight path between the accelerator and the target, and to strike against the bumper and contact plate.

Simultaneously with initiating conduction in the ignitron tube, the voltage induced in the induction coil 27 also commences a timing cycle in the timer 32. The iiap pivots into the closed position and contacts the metal plate 31 on the bumper closing a second circuit which also includes the timer. By this means the time between operation of the accelerator and a complete swing of the flap is obtained. The bumper 29 is preferably constructed of sponge rubber so that the rapidly moving ap is not damaged by contact with a rigid stop. Additionally the resilience of the sponge rubber assists the biasing spring in returning the ilap to the open position in preparation for a subsequent operation of the system. Thus the shutter assembly is recoverable or resettable and can be operated again merely by recharging the capacitor. No attention need be paid to the flap as it returns to its starting position under the biasing of the spring and rebound from the bumper. This is of importance since it is convenient to operate the shutter assembly inside a vacuum chamber. The vacuum is desirable in the described accelerator to permit high velocities in the particles and to minimize interfering pressure eifects. Since the shutter is in the vacuum, it is highly desirable that it be capable of repeated operation without attention.

The pivot point of the ap is preferably arranged close to the edge of the aperture so that the initial closing of the aperture occurs in a short time period after initial movement of the flap. Likewise it is desirable that the bumper be arranged so that the ap travels through an appreciable angle after closing the aperture so that the light path is obstructed for an appreciable period of time thereby obstructing all of the undesirable slower moving particles traveling along the Hight path. Another reason for keeping the -aperture closed for an appreciable time is to shield the target from any light from the explosion in the accelerator so as to prevent interference with photographic measurements that may be made of the impact phenomena. It will be apparent to one skilled in the art that if it is desired to keep the shutter closed -for a longer period of time than provided by spacing -the parts, a very small portion of magnetic material could be attached to the shutter so that it could be held in the closed position by a suitable electromagnet. Likewise mechanical latching arrangements could be employed to retain the flap in a closed position.

It will also be apparent to one sk-illed in the art that if a normally closed shutter were required in a particular application the positions of the bumper and the coil could be reversed so that a normally closed shutter could be operated in a similar manner to the normally open shutter described in the illustrative embodiment. Although in the preferred embodiment a shutter has been illustrated for use with a particle accelerator for obstructing an aperture through which particles may pass, it will be apparent that a shutter as described herein could also be employed to occult a light path including lenses and other optical equipment.

In a typical shutter constructed according to the principles of this invention, a coil having an inductance of approximately 50 micro-henry is actuated by a 12 microfarad capacitor charged at from 2000 to 5000 volts. A 1 x 11/2 inch shutter made of aluminum approximately 0.15 inch thick is shut in from to 500 micro-seconds depending on the voltage to which the capacitor is initially charged. Other operating speeds can be obtained by varying the mass of the shutter or the charging voltage on the capacitor.

It is to be understood that the above described examples are merely illustrative of the application of the principles of this invention. Those skilled in the art may readily devise other variations that will embody the principles of the invention. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specically described.

What is claimed is:

1. An electr-ic shutter assembly comprising:

a non-magnetic substantially at metal ap mounted for movement between a rst position and a second position;

a non-magnetic conductive coil adjacent said flap in the iirst position and insulated therefrom, said coil being aligned with said iiap so that a current in said coil will induce an eddy current in said ap so that the eld of the eddy current and the iield of the coil current interact to repel said flap;

means for resiliently biasing said flap toward said coil;

and

means for passing a predetermined current through said c-oil at a predetermined time.

2. A shutter assembly comprising:

a member having an opening therein;

a non-magnetic conductive flap pivotally mounted adjacent to the opening;

a non-magnetic conductive coil adjacent said flap and having an axis normal to the surface of said ap;

means for passing a predetermined current through said coil at a predetermined time whereby the current induces an eddy current in said flap and causes pivotal movement of said ilap away from said coil.

3. A shutter assembly as defined in claim 2 wherein said means for passing a current comprises:

an electric capacitor connected with said coil;

means for controllably charging the capacitor to a selected voltage; and

switch means for complet-ing a circuit including said coil and said capacitor whereby current will ow therethrough.

4. A shutter assembly as defined in claim 2 wherein said ap is in a position remote from said aperture in a lirst position and obstructs the opening when pivotally moved away from said coil.

'5. A shutter `assembly for obstructing the ight path of a particle in an electrically operated particle accelerator comprising:

a member having an aperture on the ight path;

a non-magnetic metal flap pivotally mounted on said member adjacent the aperture so as to be remote from the iiight path in a first position and obstructing the flight path in a second position;

a non-magnetic conductive coil having an axis normal to the plane of said flap and insulated therefrom for inducing an eddy current in said ap;

means for resiliently biasing said flap toward said coil in said first position;

a current source connected with said coil for passing a large current therethrough whereby the field of the coil current and the field of the eddy current interact to repel said flap from the rst position to the second position;

means for initiating the current passage in response to operation of the accelerator; and

means for sensing the actuation of said ap.

6. A particle separator comprising:

a particle accelerator for projecting particles along a ight path;

a member having an aperture on the flight path;

a flap pivotally mounted adjacent the aperture for movement between an open position remote from said flight path and a closed position obstructing the flight path;

means for biasing said flap in `the open position;

coil means adjacent the flap for inducing an eddy current therein; and

means for passing a current through said coil in response to operation of said accelerator.

7. An accelerator comprising:

means for supporting a plurality of particles;

explosive means for accelerating a number of said particles in a group along a ilight path wherein extraneous particles of the accelerator may be accelerated therewith;

electric means for actuating `said explosive means;

obstructing means -for blocking the flight path at a predetermined time after actuation of said explosive means; and

induction means for actuating said obstructing means in response to said electric means.

8. The accelerator of claim 7 wherein said obstructing means comprises:

a non-magnetic electrically conductive flap mounted for pivotal motion to a ight path obstructing position;

a coil mounted adjacent the ilap to repel the ap when the coil is supplied with electric current;

a capacitor for supplying electric current,

switch means responsive to said induction means for coupling the capacitor Ito the coil, and

means for controllably charging the capacitor to control the rate of motion of the ap.

9. An accelerator comprising:

a guide Itube;

meais for supporting a particle adjacent said guide tu e;

a metal Wire adjacent said means for supporting;

means for electrically exploding said wire so that metal vapor ows through said guide tube;

a member having an aperture aligned with said guide tube; and

recoverable shutter means for obstructing the aper- -ture at a predetermined time. 10. An accelerator as delined in claim 9 wherein said shutter means comprises:

a non-magnetic member mounted for movement between a position remote from said aperture and a position obstructing said aperture;

eddy current means for biasing said member toward the position obstructing said aperture; and

means for biasing said member toward the position remote from said aperture.

11. A particle separator comprising:

an electrically operated accelerator for projecting particles having a range of velocities along a ilight pa-th;

a shutter assembly for passing higher velocity particles and obstructing lower velocity particles, said shutter assembly comprising:

a member having an aperture on the ight path;

a non-magnetic substantially Hat metal ap pivotally mounted adjacent the aperture for movement between an open position remote from `the flight path and a closed position obstructing the flight path;

means for resiliently biasing said ap in the open position;

a non-magnetic current coil adjacent the flap and insulated therefrom and having an axis normal to the plane of said ap in the open position;

a capacitor having one side in electrical connection with said coil;

means for charging the capacitor to a controllably -variable voltage;

switch means in the coil circuit for connecting the other side of said capacitor to said coil whereby a current can ow therethrough;

inductance means for sensing operation of said accelerator and actuating said switch means in response thereto; and

timer means for sensing the time between operation of rthe accelerator and movement of the flap into the closed position.

References Cited by the Examiner UNITED STATES PATENTS 7/ 1946 MacNeille 84-61 X 5/1965 Ford et al. 95-53 

7. AN ACCELERATOR COMPRISING: MEANS FOR SUPPORTING A PLURALITY OF PARTICLES; EXPLOSIVE MEANS FOR ACCELERATING A NUMBER OF SAID PARTICLES IN A GROUP ALONG A FLIGHT PATH WHEREIN EXTRANEOUS PARTICLES OF THE ACCELERATOR MAY BE ACCELERATED THEREWITH; ELECTRIC MEANS FOR ACTUATING SAID EXPLOSIVE MEANS; OBSTRUCTING MEANS FOR BLOCKING THE FLIGHT PATH AT A PREDETERMINED TIME AFTER ACTUATION OF SAID EXPLOSIVE MEANS, AND INDUCTION MEANS FOR ACTUATING SAID OBSTRUCTING MEANS IN RESPONSE TO SAID ELECTRIC MEANS. 